Frosting

One 10-ounce bag peanut butter chips

2/3 cup heavy cream

Kosher salt

Chopped salted roasted peanuts, for garnish

How to Make It

Step 1 Make the custard

In a medium saucepan, combine the milk with the vanilla extract and banana and bring to a simmer. Remove from the heat and let stand at room temperature for 1 hour (or refrigerate overnight). Return the mixture to a simmer, then strain through a sieve into a heatproof measuring cup; discard any solids.

Step 2 Make the custard

In a large bowl, combine the egg, egg yolk, sugar, cornstarch and salt and whisk until thickened and smooth. While whisking constantly, gradually whisk in 1/4 cup of the hot milk to temper the eggs, then gradually whisk in the remaining milk until combined.

Step 3 Make the custard

Pour the egg-and-milk mixture into the saucepan and cook the custard over low heat, whisking constantly, until thickened, about 8 minutes. Strain the custard through a sieve into a bowl. Press a piece of plastic wrap directly on the surface of the custard and refrigerate until chilled, at least 1 hour.

Step 4 Meanwhile, make the cupcakes

Preheat the oven to 350° and line a 12-cup muffin tin with paper liners. In a medium bowl, whisk the flour with the baking powder and salt.

Step

Step 5 Meanwhile, make the cupcakes

In a large bowl, using a handheld electric mixer, beat the butter with the peanut butter, granulated sugar and brown sugar at medium-high speed until fluffy, about 3 minutes. Beat in the eggs, one at a time, then beat in the vanilla. At low speed, beat in half the flour mixture, then all the milk, followed by the remaining flour mixture.

Step 6 Meanwhile, make the cupcakes

Fill the prepared muffin cups with the batter until almost full and bake for about 20 minutes, until a toothpick inserted in the center of the cupcakes comes out clean. Transfer the cakes to a wire rack and let cool completely.

Step 7 Make the frosting

Put the peanut butter chips in a large heatproof bowl. In a small saucepan, bring the heavy cream to a simmer, then pour it over the peanut butter chips and let stand for 5 minutes. Add a pinch of salt and whisk the frosting until smooth; let cool, stirring occasionally, until spreadable.

Step 8 Make the frosting

Transfer the banana cream into a piping bag fitted with a large round tip. Insert the tip into the top of each cupcake and fill with some of the cream. Frost the cupcakes and garnish with peanuts.